"You will kill a man,"
"and take his stuff."

Seriously though, since I prefer sandboxes, whenever this has come up I just drop hints about things already happening outside of the characters' immediate awareness or control.

"What's really going to bake your noodle later is ...  would you still have broken it if i hadn't said anything."
- The Oracle: Matrix.

Simply put, there is the idea, that the fortune-telling itsellf will cause the characters to start on a path, that will make them cause the foretold events, or part of them.
Like trying to stop an assassination, only to end up killing the sleepwalking target ....
Or trying to stop it, by rounding up the usual suspects, and being to rough while doing so, so they cause the reason for the assassination among those ...
Or ... rounding up the usual suspects, and find that these really is good people ... and proof that the one about to get assassinated really is scum "worthy" of being ass... killed.

I only use them as plot hooks, either by pointing the player in a direction and making something close enough to the prediction happen without making it absolute. Even if a player wants to directly view the future, it will be hazy and slightly vague in a way that gets interest going for whatever they wanted to do anyway.

So a player who is predicted to slay a dragon might end up slaying an actual dragon, killing a human with a large dragon tattoo, or accidentally crush the paper dragon in the parade. A player who is predicted to have wealth may have it offered criminally, or be given a personal reason to donate away personally achieved wealth, or some other additional complication (never taken by fiat) in a way that provides more stuff to do.

I did do the 'foresee your own death' one time with a player that I knew could handle it, but I wouldn't do it with just any player.

I handle them similar to Earthly fortune telling, so mechanically they can be all over the map. Further, certain methods favor different strengths, like forecasts, overviews, personality analysis, past analysis, etc. And then at some point it is like meteorology -- getting a bird's or satellite's eye view from above -- large trends show patterns, and if uninterrupted suggest XYZ.

But then I also divide what is within human purview and general large aspects. So if i reveal that a large snow front is coming during a rather pleasant streak of weather, human choice determines how bad the snow affects them. So PCs are passive recipients to events. And then there's the following this path leads to a dead-end arroyo, during rainy season. So PCs here would be active participants in their own events.

And then there's my favorite, when divination is starting to be overused: "as you keep gazing into the threads of fate and destiny, eventually fate and destiny gaze back at you." So aspect related events are generally so big they are going on their own accord. But if you keep scrying to stay one step ahead, you eventually attract the attention of said big aspects putting events in motion. To attract the attention of the greater powers is not a welcome outcome and tends to make diviners more cautious (and explains why they don't/won't/can't use it to win lotteries).

I roll 1d10.

1-9 it's fucking bullshit. I make up some vague shit that could be true, but isn't.

10 its true. I make up some vague shit that hapens to be true.

My players never know if the seer got it right by chance or because fortune telling works. Just like RL

I came to like "Ask one yes/no question per success".

I use the Events tables from OA, and roll the events for the entire year. One reason I do this is in case the PCs try their hand at divination. I'll actually have something tangible for them to divine.

As a rule of thumb, I treat this kind of thing like the weather: No matter how skilled the forecaster, no matter how accurate his or her tools might be, no matter how obvious the answer might seem to be, there's still a good chance of the prediction turning out wrong. VERY wrong. Of course the chance that it might be right makes it a tempting gamble...

In Stupor Mundi/Merrie England, we gave a successful Fortune Telling a number of Fortune Points, which are effectively Hero Points/Fate Points that can be spent by the PC, or the GM, to help to achieve the result. So, a prediction that "You will fall at Paris" might mean that a Fortune Point is spent when riding through Pairs for the horse to rear up and the PC falls off, or  a battle might be lost at Paris, or whatever.

Generally some kind of random table, where I (as GM) will incorporate some element of it into the future of the game if I find it really interesting; if not, well, divination is an inexact science...

..unless of course it is meant to be exact and accurate in the setting. In that case I'm much more careful and would probably not rely on a random table.